17.6: Human Interference with Shorelines
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There are various modifications that we make in an attempt to influence beach processes for our own purposes. Sometimes these changes are effective, and may appear to be beneficial, although in most cases there are unintended negative consequences that we don’t recognize until much later.
An example is at the beach near Comox (described above), which has been armoured with rip-rap and concrete blocks in an attempt to limit the natural erosion that is threatening the properties at the top of the cliff (Figure 17.3.4). As already noted, the unintended effect of this installation will be to starve Goose Spit of sediment. As long as the armour remains in place, which might be several decades, there is a risk that the spit will start to erode, which will affect many of the organisms that use that area as their habitat, and many of the people who go there for recreation.
Seawalls, like the one around Vancouver’s Stanley Park (Figure 17.5.1), also help to limit erosion and can be very pleasant amenities for the public, but they have geological and ecological costs. When a shoreline is “hardened” in this way, important marine habitat is lost and sediment production is reduced, and that can affect beaches elsewhere. Seawalls also affect the behaviour of waves and longshore currents, sometimes with negative results.
Exercise 17.5 Crescent Beach Groynes
This diagram shows the same area illustrated in Figure 17.5.4 at Crescent Beach in Surrey, B.C. Based on information that you can find on the Internet about the function of groynes, determine which way the prevailing longshore current is moving at this location.
Beach and groyne locations at Crescent Beach, Surrey [SE]
Contributors
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Physical Geology by Steven Earle used under a CC-BY 4.0 international license. Download this book for free at http://open.bccampus.ca.